Electric Power Steering Smooth Mode Switching
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Solution Overview
Problem
During autonomous driving, driver interventions in the steering wheel operation are not fully reflected, leading to feelings of strangeness and discomfort due to abrupt changes in steering angle and assist control command values, which are not smoothly switched between, causing unnatural steering behavior and excessive responses.
Innovation Solution
An electric power steering apparatus with an ECU that generates control signals based on a target vehicle trajectory, featuring a steering angle control section, assist control section, and a switching determination/gradual change gain generating section to smoothly switch between automatic and manual steering modes, using proportional and PI control to manage steering angular velocity and reduce vibrational frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If gradual change gain is applied to switch between steering angle control and assist control, then abrupt changes in command values are suppressed, but driver intervention is not fully reflected and steering responsiveness deteriorates
Solution Approach 1:
The patent applies dynamic adjustment of gradual change gain based on driving state. The control section switches between gradual change control and non-gradual change control depending on whether the vehicle is in autonomous driving mode or manual driving mode, making the system adaptable to different operational contexts rather than using a fixed gradual change mechanism
Solution Approach 2:
The patent changes the control parameter (gradual change gain) based on the driving mode. In autonomous driving mode, gradual change gain is applied to ensure smooth transitions; in manual driving mode, the gain is adjusted or removed to prioritize driver input responsiveness, thereby resolving the contradiction between smooth switching and steering responsiveness
2Stability of the object's composition
If steering angle control command value is restricted by gradual change gain, then abrupt changes are suppressed, but integral values accumulate in I control and excess command values are generated
Solution Approach 1:
The patent incorporates feedback control where the actual steering angular velocity is measured and compared with the commanded velocity. The PI controller uses this feedback to adjust the motor current command, preventing excessive integral accumulation by continuously correcting the error between desired and actual steering rates
Solution Approach 2:
The control system dynamically adjusts the gradual change gain based on the current driving mode. When manual intervention is detected, the system transitions from gradual change control to direct control, preventing the accumulation of excessive integral values while maintaining command stability during autonomous operation
3Extent of automation
If switching between steering angle control and assist control is implemented, then autonomous driving control is achieved, but driver intervention feels unnatural and causes discomfort
Solution Approach 1:
The patent implements dynamic switching between control modes based on driver input detection. When the driver operates the steering wheel during autonomous driving, the system transitions from autonomous control to manual control mode, making the system behavior adaptive to driver intent and eliminating the unnatural feeling of rigid mode switching
Solution Approach 2:
The control section acts as an intermediary that detects driver steering operations and mediates the transition between autonomous and manual control modes. This intermediary function smooths the switching process by detecting driver intent and appropriately adjusting the control strategy, thereby improving driver comfort during mode transitions
Data Source
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AI summary
When a steering operation by a driver intervenes during autonomous driving of a vehicle, the intervention operation is fully reflected and a feeling of strangeness and a feeling of discomfort that may be given to the driver are reduced. An ECU of an electric power steering apparatus includes: a steering angle control section 200 to which a steering angle command value is input to control a steering angle; an assist control section 147 to which an assist map gradual change gain is input to output an assist control output gradual change gain; and a switching determination/gradual change gain generating section 145 that generates a gradual change gain, by which steering angle control output and assist control output are multiplied, and multiplies the gradual change gain to make a switching determination between a steering angle control mode by the steering angle control section 200 and an assist control mode by the assist control section 147. The steering angle control section 200 has a position control section 208, a steering angular velocity control section 212, and steering intervention compensating and steering-wheel vibration suppressing means 220.